Sheet carrying apparatus having sheet pressing mechanism, and sheet carrying method using sheet carrying mechanism

ABSTRACT

A sheet carrying apparatus having a sheet pressing mechanism according to an embodiment of the invention includes: a paper supply tray in which sheets for printing an image thereon are stacked; a pickup roller which is abutted from above against a sheet on a top layer of the sheets stacked in the paper supply tray, then rotates and move the sheet on the top side; and a holding plate which presses the top layer sheet from above in a part where the pickup roller is abutted against the top layer sheet.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from Provisional Application No. 61/170571 filed on Apr. 17, 2009, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a sheet carrying apparatus and particularly to a sheet carrying apparatus that can securely supply a sheet that tends to float such as a reuse sheet, to an image forming apparatus or the like.

BACKGROUND

In an apparatus for printing an image such as an image forming apparatus, facsimile or copier, sheets for printing needs to be supplied and the sheets are usually automatically supplied by a sheet carrying apparatus.

The sheet carrying apparatus needs to securely carry sheets one by one. To this end, the one sheet on the top side in a sheet tray where sheets are housed needs to be securely carried out. A rotating pickup roller is abutted, usually from the top side, against a bundle of sheets housed in a supply sheet tray, thus carrying one sheet.

Meanwhile, in view of resources, reuse of sheets is considered and used sheets are actually used in some cases. In such cases, if a sheet to be reused is folded or creased in the previous use, it often happens that this sheet floats in a sheet bundle at the time of reuse.

If such a sheet is housed in the ordinary supply sheet tray and carried, the sheet may float and may not be normally carried, compared to ordinary sheets.

The invention is to provide a carrying apparatus that can securely carry such a recording sheet.

Meanwhile, an image forming apparatus is known in which sorting of reusable used sheets is automated. A technique of arranging a correction roller upstream of a scanning roller, correcting folding or creases generated in a used sheet and thus preventing a jam is known, as disclosed in JP-A-2000-255909.

Also, an apparatus for housing used sheets is known which is provided in a lower part of an electrographic apparatus and in which a table (elevator) having a bundle of used sheets placed thereon is moved upward and the sheets are pressed from below, thus reducing the quantity of curling, as disclosed in JP-A-2002-128373.

However, even these apparatuses cannot significantly reduce the quantity of curling of reuse sheets. When these reuse sheets are actually used for printing an image, curling, folding or creasing occurs and the sheet on the top layer floats. Therefore, it is difficult to stably supply reuse sheets one by one from a paper supply tray housing the reuse sheets.

The invention is to provide a sheet carrying apparatus having a sheet separation mechanism which can stably supply reuse sheets and the like one by one even if such curling is generated to a certain extent.

SUMMARY

According to an aspect of the invention, a sheet carrying apparatus having a sheet pressing mechanism includes: a paper supply tray in which sheets for printing an image thereon are stacked; a pickup roller which is abutted from above against a sheet on a top layer of the sheets stacked in the paper supply tray, then rotates and move the sheet on the top side; and a holding plate which presses the top layer sheet from above in a part where the pickup roller is abutted against the top layer sheet.

According to another aspect of the invention, a sheet carrying method using a sheet pressing mechanism includes: pressing a sheet on a top layer of sheets stacked in a paper supply tray in which sheets for printing an image thereon are stacked, from above by a holding plate; and abutting a pickup roller against the sheet on the top layer from above and rotating the pickup roller, in a part that is not pressed by the holding plate, and thus moving the top layer sheet.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a configuration where a sheet carrying apparatus according to an embodiment of the invention is applied to an image forming apparatus.

FIG. 2 is a perspective view showing the structure of the sheet carrying apparatus according to the embodiment of the invention.

FIG. 3 is a view for explaining the relation between a paper supply tray, stacked sheets, a pickup roller and a holding plate in the sheet carrying apparatus according to the embodiment of the invention.

FIG. 4A is a plan view showing the structure of the lower side of an exemplary holding plate.

FIG. 4B is a sectional view showing the structure of the lower side of the exemplary holding plate.

FIG. 5 is a flowchart for explaining the operation of the sheet carrying apparatus according to the embodiment of the invention.

FIG. 6 shows the sectional structure of the holding plate used in the embodiment of the invention.

FIG. 7A shows the planar shape of another exemplary holding plate used in the embodiment of the invention.

FIG. 7B shows the planar shape of still another exemplary holding plate used in the embodiment of the invention.

DETAILED DESCRIPTION

Hereinafter, an embodiment of a sheet carrying apparatus according to the invention will be described with reference to the drawings.

FIG. 1 shows a configuration where a sheet carrying apparatus 10 according to an embodiment of the invention is applied to an image forming apparatus 11. FIG. 2 shows a perspective view of this sheet carrying apparatus 10.

The sheet carrying apparatus 10 has: a paper supply tray 13 in which sheets 12 for printing are stacked; a U-shaped holding plate 14 which presses the stacked sheets 12 from above by its own weight; pickup rollers 17 a and 17 b which move one sheet 16 on the top side of the stacked sheets in a U-part 15 of the holding plate 14; plural carrying rollers 18 which continue carrying the one sheet 16 that is moved, to a predetermined position; and a frame 18 a which supports these roller.

The stacked sheets 12 are, for example, sheets to be reused which are used once and then have toners removed or are reversed so that the used side faces back. A paper supply sensor 18 s detects that the top layer sheet 16 is carried to the carrying rollers. Moreover, a registration sensor 19 s detects that the top layer sheet 16 is carried to a registration roller 19. The pickup rollers 17 a and 17 b and the carrying rollers 18 are rotated by a motor M to carry the top layer sheet 16 in the direction of an arrow 16 a.

The sheet carried by the group of carrying rollers 18 is aligned by the registration roller 19. In an image forming, developing and transfer unit 21 shown in FIG. 1A, a latent image formed on a rotating photoconductive drum 22 is developed and then transferred to the carried sheet 16. The image is heated and fixed by a heating unit 23.

That is, in the image forming, developing and transfer unit 21, uniform charging by a charger 24 and selective exposure 25 are carried out around the photoconductive drum 22, and the formed electrostatic latent image is developed with a toner in a developing device 26. The toner-developed image is transferred to the carried sheet 16 and is carried to the heating unit 23. In the heating unit 23, the sheet 16 having the transferred image is nipped between a heating roller 27 a and a pressurizing roller 27 b and then heated so that the image is fixed. The sheet 16 to which the image is fixed is discharged outside the image forming apparatus 11.

In this manner, the sheet carrying apparatus 10 in the image forming apparatus is an apparatus supplying a sheet (recording sheet) to which, for example, an image developed with a toner is to be fixed.

FIG. 3 shows how the top layer sheet 16 is moved from the paper supply tray 13 in the sheet carrying apparatus 10. At the time of paper supply, the stacked sheets 12 housed in the paper supply tray 13 are pushed upward, for example, by springs 31 a and 31 b, as indicated by an arrow 32. Therefore, when the pickup roller 17 a is rotating, the top layer sheet 16 is abutted against the lower side of the holding plate 14. A turning edge 14 e is turned below about a supporting shaft 34 by the holding plate 14's own weight and the top layer sheet 16 is pressed.

When there are no stacked sheets 12 left, for example, a solenoid 36 connected with a tension spring 35 provided on the holding plate 14 becomes electrified. Thus, after the holding plate 14 is fixed and held, the paper supply tray 13 is moved downward, the direction opposite to the arrow 32, and sheets are supplied thereto. After that, the paper supply tray 13 rises again and the electrification of the solenoid 36 is canceled. The holding plate 14 is abutted against the top layer sheet 16 of the stacked sheets 12, restraining the floating of the sheet 16.

The length ML of the holding plate 14 in the moving direction of the top layer sheet 16 need not be as long as the length SL of the stacked sheets 12, as shown in FIG. 3. It suffices that the length ML is approximately half the length SL from the edge where the top layer sheet is sent out. The length ML of the holding plate 14 may be shorter than this length.

The holding plate 14 is made of, for example, a resin and has a thickness of, for example, approximately 5 to 6 mm. In many cases, the thickness may be approximately 3 to 10 mm. If the holding plate 14 is very heavy, it is difficult for the pickup roller 17 a to move the top layer sheet 16. On the other hand, if the holding plate 14 is too lightweight, the effect of preventing the top layer sheet 16 from floating is reduced. It is preferable to decide the weight of the holding plate so that both the appropriate movement of the top layer sheet and the floating prevention effect can be realized. If the holding plate 14 is made of a metal such as iron, its weight can be increased.

If a reuse sheet to be used floats to a large degree, the weight of the holding plate may be changed or an additional weight may be added onto the holding plate so as to increase the weight of the holding plate. Thus, the floating prevention effect can be enhanced.

Since the top layer sheet 16 is moved by the pickup roller 17 a, it is preferable that the frictional force between the pickup roller 17 a and the top layer sheet 16 is large, whereas the frictional force between the top layer sheet 16 and the holding plate 14 is small. Thus, it is preferable that grooves 41 are provided on the lower side of the holding plate 14, parallel to the direction of the movement of the top layer sheet 16, as shown in FIG. 4A and FIG. 4B. Thus, the frictional force between the holding plate 14 and the top layer sheet 16 can be reduced.

In any case, a pressing force to the top layer sheet 16 and the stacked sheets 12 from above by the holding plate is necessary in order to reduce the floating, but it is preferable that the lateral frictional force is as small as possible. For example, it is also possible to reduce the frictional force by processing the lower side of the holding plate to facilitate sliding.

Hereinafter, the operation of the sheet carrying apparatus according to this embodiment of the invention will be described with reference to the flowchart shown in FIG. 5. This sheet carrying apparatus is used for an image forming apparatus and for printing an image. In the image forming apparatus, formation of other latent images, development, transfer of developed images to sheets, discharge of sheets and the like are carried out in parallel.

In. ACT A501, first, it is detected whether a paper supply instruction is given or not. If a paper supply instruction is given in ACT A501, the pickup roller 17 a is rotated in the direction shown in FIG. 3 in the next ACT A502 and the top layer sheet 16 is moved in the direction of the arrow 16 a (ACT A503). At this time, the weight of the holding plate 14 is applied onto the top layer sheet 16. Even if the sheet floats, the floating is restrained by the holding plate 14.

The top layer sheet 16, moved by the rotation of the pickup roller 17 a and existing the paper supply tray 13, is carried by the plural carrying rollers, aligned by the registration roller 19, and sent to the image forming, developing and transfer unit 21. In the image forming, developing and transfer unit 21, the sheet 16 having an image transferred thereto has the image fixed by the fixing unit 23 and is then discharged outside the image forming apparatus. The paper supply tray 13 is constantly pushed upward from below. As the top layer sheet is carried, the next sheet below that sheet now becomes the top layer sheet.

Meanwhile, in the sheet carrying apparatus, it is detected in ACT A504 whether the sheets in the paper supply tray 13 are gone or not. If the sheets in the paper supply tray 13 are not gone, the processing shifts to ACT A502 and the pickup roller 17 a is rotated. The top layer sheet 16 is moved in ACT A503.

If the sheets in the paper supply tray 13 are gone in ACT A504, the rotation of the pickup roller 17 a is stopped in ACT A505. In the next ACT A506, the solenoid 36 is electrified to actuate the tension spring 35. The holding plate 14 is fixed and held. The downward turning of the turning edge 14 e of the holding plate 14 is restrained.

In ACT A507, the paper supply tray 13 moves downward against the springs 31 a and 31 b and reuse sheets are supplied (A508). As the supply of sheets is completed, the paper supply tray 13 in which the stacked sheets 12 are placed rises in ACT A509 and stops in the state where the top layer sheet 16 is abutted against the pickup roller 17 a.

In ACT A510, the electrification of the solenoid 36 is switched off and the fixation and holding of the holding plate 14 is canceled. The pressing by the holding plate 14 from above by its own weight is resumed.

In the next ACT A511, it is detected whether an instruction to stop paper supply is given or not. If an instruction to stop paper supply is given, the processing returns to ACT A501 to wait for a next paper supply instruction.

Meanwhile, if an instruction to stop paper supply is not given in ACT A511, the processing returns to ACT A502 to rotate the pickup roller 17 a and the next top layer sheet 16 is moved (A503). Also at this time, of course, the downward pressing force by the holding plate 14 is applied to the top layer sheet 16.

In this manner, by applying the pressing force by the holding plate 14 to the stacked sheets 12 and the top layer sheet 16 from above, it is possible to restrain floating of sheets in the case of using reuse sheets as recording sheets.

The edge side of the holding plate used in the above embodiment can be curved as shown in FIG. 6. This holding plate 61 has a section 62 where an edge part to be abutted against a substantially central part of the top layer sheet is curved downward. That is, a part of the cross-section of the turning edge 14 e to be abutted against the top layer sheet is curved downward. This curving has an advantage that the floating can be smoothly eliminated when the top layer sheet moves in the direction of an arrow 63.

The holding plate used in the above embodiment is U-shaped as shown in FIG. 4A. However, a holding plate 71 having slant lines 71 a and 71 b in a part corresponding to substantially the center of the top layer sheet, as shown in FIG. 7A, may also be used. The use of the holding plate 71 of this shape has an advantage that when the top layer sheet is carried, the floating can be reduced from the center of the sheet.

A holding plate 73 as shown in FIG. 7B can be used as well. This holding plate 73 has a notched part 72 that is not U-shaped but triangle-shaped. In this manner, any shape can be employed except for the part where the pickup roller 17 a is abutted against the top layer sheet 16 (indicated by the dotted line).

In the embodiment, when the paper supply tray 13 moves downward, the holding plate 14 is fixed and held by the tension spring 35 and the solenoid 36. However, a protrusion may be provided on a lateral side near the turning edge 4 e of the holding plate 14 so as to fix and hold the holding plate 14.

In the embodiment, the sheet is pressed from the top side by the holding plate's own weight. However, a spring which pulls down the turning edge 14 e of the holding plate may be provided so as to apply a downward pressing force to the sheet.

In the embodiment, one edge of the holding plate is supported by the supporting shaft provided substantially parallel to the direction of the movement of the top layer sheet, and the other edge is turned to apply a pressing force to the top layer sheet. However, a pressing force maybe applied to the top layer sheet by the entire surface of the holding plate. Although the case of using reuse sheets is described in the embodiment, the invention can be applied to the case of using new sheets.

Obviously, many modifications and variations of this invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, this invention may be practiced otherwise than as specification. 

1. A sheet carrying apparatus having a sheet pressing mechanism, comprising: a paper supply tray in which sheets for printing an image thereon are stacked; a pickup roller which is abutted from above against a sheet on a top layer of the sheets stacked in the paper supply tray, then rotates and move the sheet on the top side; and a holding plate which presses the top layer sheet from above in a part where the pickup roller is abutted against the top layer sheet.
 2. The apparatus according to claim 1, wherein the holding plate presses the top layer sheet from above by its own weight.
 3. The apparatus according to claim 2, wherein the holding plate is abutted against the top layer sheet in a part that is not the part where the pickup roller is abutted against the top layer sheet.
 4. The apparatus according to claim 3, wherein the holding plate is abutted against the top layer sheet in a part that is not the part where the pickup roller is abutted against the top layer sheet and closer to an edge in a moving direction of the top layer sheet.
 5. The apparatus according to claim 4, wherein the holding plate has a structure such that the holding plate is abutted against the top layer sheet substantially at right angles to the moving direction of the top layer sheet and with a turning edge turning about a supporting shaft provided near an edge of the top layer sheet.
 6. The apparatus according to claim 5, wherein a part of a cross-section of the turning edge to be abutted against the top layer sheet has a downward curved shape.
 7. The apparatus according to claim 6, wherein the holding plate has such a shape that a part where the pickup roller is abutted against the top layer sheet is cut out.
 8. The apparatus according to claim 7, wherein the turning edge of the holding plate has a shape including two sides slanting in the direction of the supporting shaft from a central part.
 9. The apparatus according to claim 7, wherein the holding plate has a U-shape.
 10. The apparatus according to claim 9, wherein the holding plate has a groove parallel to the moving direction of the top layer sheet, on a side to be abutted against the top layer sheet.
 11. The apparatus according to claim 10, wherein the holding plate is fixed and held at a predetermined position before the sheets are supplied to the paper supply tray, and the fixation and holding of the holding plate is canceled after the sheets are supplied to the paper supply tray.
 12. The apparatus according to claim 11, wherein the fixation and holding of the holding plate is carried out by a tension spring and a solenoid provided above the holding plate.
 13. The apparatus according to claim 12, wherein the paper supply tray rises after reuse sheets are supplied to the paper supply tray, and the pickup roller rotates after the holding plate is abutted against the top layer sheet.
 14. A sheet carrying method using a sheet pressing mechanism, comprising: pressing a sheet on a top layer of sheets stacked in a paper supply tray in which sheets for printing an image thereon are stacked, from above by a holding plate; and abutting a pickup roller against the sheet on the top layer from above and rotating the pickup roller, in a part that is not pressed by the holding plate, and thus moving the top layer sheet.
 15. The method according to claim 14, further comprising: stopping the rotation of the pickup roller when the sheets housed in the paper supply tray are gone; fixing and holding the holding plate; after moving the paper supply tray downward and supplying sheets, moving the paper supply tray upward and stopping the paper supply tray in a state of being abutted against the pickup roller; canceling the fixation and holding of the holding plate; and rotating the pickup roller and moving the top layer sheet.
 16. The method according to claim 15, wherein the holding plate is abutted against the top layer sheet in a part that is not the part where the pickup roller is abutted against the top layer sheet and closer to an edge in a moving direction of the top layer sheet.
 17. The method according to claim 16, wherein the holding plate has such a structure that the holding plate is abutted against the top layer sheet substantially at right angles to the moving direction of the top layer sheet and with a turning edge turning about a supporting shaft provided near an edge of the top layer sheet.
 18. The method according to claim 17, wherein the holding plate has a part of a cross-section of the turning edge to be abutted against the top layer sheet that has a downward curved shape.
 19. The method according to claim 18, wherein the holding plate has a U-shape.
 20. The method according to claim 19, wherein the holding plate has a groove parallel to the moving direction of the top layer sheet, on a side to be abutted against the top layer sheet. 